The separation of organic compounds from water has been an ongoing challenge for the chemical industry. Typically, techniques such as distillation, decantation, extraction, evaporation, and chromatography have been employed. These methods, however, often are energy intensive, expensive to operate, and may not be practical or economical for the recovery and purification of materials from dilute aqueous solutions. For example, chemical products such as glucose, which is isolated from biomass, and fermentation products such as lactic acid, phenylalanine, citric acid, L-amino acids, succinic acid, and ascorbic acid, typically must be separated, recovered, and purified from dilute aqueous solutions or fermentation broths. The recovery costs for such fermentation processes are often the major factor which determines their commercial success. The presence of water in chemical products also often complicates purification methods such as crystallization, waste disposal methods, such as incineration, and the recovery and recycling of solvents.
Over forty years ago, a new process was developed specifically for large scale industrial purifications. U.S. Pat. No. 2,985,589 disclosed a chromatography system involving a separation tower divided into a number of individual separation beds. These beds are connected in series, and the outlet at the bottom most bed is connected to a pump that returned flow in a continuous loop to the upper most bed. The inlet apparatus for each bed has a port connected to a downward flowing conduit. The conduits terminate in fittings attached to a rotary valve designed to control both ingress and egress of liquids into or from the inlets to each individual bed. The system is called Simulated Moving Bed (SMB) chromatography because the beds appear to be moving in a direction countercurrent to the direction of flow. There are hundreds of adsorbents which have been used for simulated moving bed systems, some of which include resins, zeolites, alumina, and silica.
Simulated Moving Bed (SMB) technology represents a variation on the principles of high performance liquid chromatography. SMB can be used to separate particles and/or chemical compounds that would be difficult or impossible to separate by any other means. Furthermore, SMB technology represents a continuous process which provides a significant economic and efficiency advantages in manufacturing operations compared to batch typical batch separation methods including crystallization and stepwise chromatographic separations.
The continuous nature of SMB operation is characterized by very brief flow stoppages during the port switchovers in successive process steps. However, since all input and output conduits briefly stop at the same time, there are no significant pressure drops or surges in the system. Indexing of mechanical rotors is designed to effect rapid switchovers, even on very large industrial machines. Further, strategy in the design of process configuration is largely dictated by the affinity and release characteristics of bound species to the solid substrate, exclusion properties of unbound species, the bed volume required to obtain separation of by-product, and other factors.
There are more than 200 issued patents on modifications of SMB technology that disclose improvements in separation efficiency generally, or in particular applications, enhanced purity and yield in the final products, or reduction in required volume desorbent. For example, in one variation disclosed in U.S. Pat. No. 5,156,736, separations are performed in a single bed preserving the principles of SMB by interposing at various levels in the bed a series of crossectionally functional collection and distribution means for adding feedstock and recycled process liquid, collecting raffinate, distributing eluent, and recovering extract product. Equilibrium is established in the system by very precise flow and pressure control.
U.S. Pat. No. 4,333,740 discloses an absorptive process for separating water from a feed mixture comprising ethanol and water, which comprises contacting the feed mixture with an adsorbent comprising corn meal, selectively adsorbing substantially all of the water to be separated to the substantial exclusion of the ethanol, and thereafter recovering high purity ethanol. The process employs a countercurrent moving bed or simulated moving bed countercurrent flow system.
In U.S. Pat. No. 5,755,967 discloses the use of a new composite membrane and a method for recovery of acetone and butanol using pervaporation. In the technique molecules are selectively adsorbed by a membrane and are caused to diffuse across the membrane through a driving force such as vacuum.
U.S. Pat. No. 7,166,460 discloses a bioprocess engineering solution for a product removal process for use in biofermentation. The invention discloses a process for withdrawing an aliquot of broth from a biofermentation vessel during at least a portion of the biofermentation, removing biocatalyst and water, chromatographically separating biofermentation products from the withdrawn broth using water as an eluent, and returning the remaining components of the broth back to the biofermentation vessel. The continuous chromatic separation process is disclosed to be counter-current chromatography or simulated counter-current chromatography, including simulated moving bed chromatography. However, the reference states that process chromatography methods are unable to selectively separate biofermentation products and recycle the other media components to the biofermentor. This occurs because a portion of the eluent required to drive chromatographic separation would accumulate in the biofermentor, reducing its capacity.
US Publication No. 2010/0099155 discloses apparatuses and processes for the removal and production of fermentation prepared one or more volatile organic compounds. The apparatuses comprise a fermentor unit, a vacuum side stripper unit, and optionally one or more pressure swing adsorption unit, a dual-function column, a dividing wall distillation column, and a means for inducing phase separation of a mixture of volatile compounds and water.
Biofermentation processes provide a fermentation product stream which comprises water, ethanol, non-condensable gases such as methane, nitrogen, carbon dioxide, and hydrogen, oxygenated organic compounds and soluble biomass materials. Oxygenated chemicals such as ethanol have been traditionally produced from sugar sources, such as corn, sugarcane, molasses, etc. Other associated oxygenates produced with ethanol by fermentation often include isopropanol, propanediols, butanediols, and acetic acid. For example, it is well known that 2,3-butanediol can be produced by fermentation techniques. Examples of some species of bacteria such as Bacillus polymyxa and Klebsiella pneumoniae have been disclosed to convert both glucose and xylose into mixtures of predominantly 2,3 butanediol and ethanol. Also, the production of 2,3-butanediol has been disclosed using arabinose as a feedstock. A summary of such methods entitled, “Bulk Chemicals from Biomass”, by Jacco van Haveren, et al. was published online in Wiley InterScience. More recently, ethanol has been produced by the fermentation of gases such as carbon monoxide. The LANZATECH Process (Available from LanzaTech Inc., Parnell Auckland, New Zealand) uses microbial gas fermentation to convert any carbon monoxide containing gases produced by industries such as steel manufacturing, oil refining and chemical production, as well as gases generated by gasification of forestry and agricultural residues, municipal waste, and coal into valuable fuel and chemical products to produce ethanol and other molecules, such as 2,3-butanediol. A description of the LANZATECH microbial gas fermentation process is disclosed in U.S. Publication No. US20100323417 and in U.S. Pat. No. 8,119,378, which are hereby incorporated by reference.
Co-pending U.S. application Ser. No. 13/478,160, filed May 23, 2012, discloses an SMB process for recovering ethanol and 2,3 butanediol derived from fermentation effluent, wherein during the SMB cycle, at least one of the adsorption beds is regenerated with methanol, ethanol, propanol and the stationary phase agent is a fluorinated carbon adsorbent.
The known methods for dewatering organic compounds are limited primarily to organic acids and typically utilize a strong charge-charge interaction between the acid and adsorbent, such as ion-exclusion, as the primary separation mechanism. Because such charge-charge interactions are weak or non-existent for neutral organic compounds, these methods are not, in general, applicable for dewatering organic compounds without carboxyl substituents.